UseBB is completely licensed under the GPL. The license states what you can do (and must do if you modify and redistribute).

Basically, you can modify and redistribute but only again under the terms of the GPL, stating what you have modified to the code. You cannot take UseBB's code, modify it and release it as/for a commercial or freeware (non Open Source) product.

As far as I know about GPL 2, you must retain the copyright or in any case make it so that it still states the UseBB Team/Project. The GPL states:

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1. You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program.

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2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions: ...

An appropriate copyright notice would be one that states who has the actual copyright, which in most of the code's case is this project's contributors.

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2. ...

a) You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.

And you must state which changes you made and what time. This may be hard, but can as far as I know be done by making a version control system (such as SVN) and its history publicly viewable.

I agree the GPL can be difficult to understand, but you will have to in order to alter and distribute UseBB.

So to make clear, you cannot remove all copyrights, or redistribute this under a license other than or not compatible with GPL 2.